4.1 | Synthesis of PEG-lipid derivatives
End-functionalized PEG-lipids, such as DPPE-PEG-OMe, DPPE-PEG-TAMRA, DPPE-PEG-biotin, and DPPE-PEG-PyDTP, were synthesized from commercially available bifunctionalized PEGs and DPPE (Figure 1A and 1B; also see Supporting Information Figure S1 and S2). Details of the synthesis are provided in the Supporting Information. All products were identified using 1H-NMR spectroscopy.